Waterjet and ShopBot


I started off with the waterjet by making many flexures. I did a little research on flexure designs and settled first on a concept that looked robust and provided symmetric linear motion. I didn't do any calculations on stiffness before I started, so I just made my best guess as to a fairly flexible beam size of about 2mm by 30mm by 1/8" thick Al.

It turned out that these beams were much too stiff and I narrowed them down to 1mm by 45mm for a successive version. This deflected much more nicely and I secured its anchor points to my bed frame so I could accurately measure deflections and hear it vibrating at its audible resonant frequency. I would like to make a flexure instrument that you can pluck or strum to create chords from the beam frequencies. I also made a cantilever flexure, but this did not perform as well as I would have like because the material was too thin to elastically recover from too much deflection.

I also made a spring, but it also did not perform superbly. I think I will have to use at least 1/2" Al for future flexure tests.
I had some problems with my Al stock shifting during the waterjetting. I'll remember to always use weights in addition to clamps to keep everything fixed.


I decided to make a pair of glasses for myself with the waterjet. I had some 1/4" blue-tinted glass lying around and I wanted to try cutting that. It was mentioned that the OMAX could cut glass, but I had been skeptical at the time that such a powerful cut could also deal with the delicated glass. I placed a 1/2" piece of scrap plywood undernead the glass to prevent the jet from expanding too much when it encountered a change in impedance. I also used the low pressure setting to pierce the glass in order to prevent it from shattering. The result was quite good. Only a few tiny flakes had chipped off the underneath of the glass. The 1/4" thick Al frames were relatively straightforward after I had sized their design to my head.

I made the IDs and ODs the same, but I had to do some post proccessing sanding to get the pieces to fit, so I'll have to remember to give some clearance next time. I expoxied in some stiff wires to hold the glasses around my ears. Success!
I also cut a $ sign out of 1/32 Al for my 2.008 class.


Next, I made some cranks for my unicycle. I was unhappy with the ones I had fabricated via conventional machining before and realized that I could deal with the whole thing quite easily with the waterjet. All that is now required is a tap for the pedal and a bolt hole to clamp down on the unicycle axle. Notice the very jagged finish on the side of the waterjet crank. Although I set the OMAX settings to cut thick 1/2" Al, it still had troubles, and I'll have to set a slower speed manually next time. On my first attempt at cutting these, the waterjet head halted because I had placed my stock too close to the edge of the bed. Lesson learned.

Magnetic Axles:

While brainstorming ideas for things I could make on a waterjet, I kept pondering ways to make rotating parts. Axles are obviously difficult because the cuts are always straight, and for large thicknesses, the kerf draft get unacceptably large. So, why not use some strong, cylindrical NIB magnets? I had some 1/4" by 1/4" ones lying around and cut some quick parts to hold them. The result was promising: The magnets located the rods accurately and held them snugly enough to smoothly rotate the rods with out breaking the connection. I have not yet come up with an interesting application for these, but I will someday.


Next, I moved to the ShopBot. I sketched up a cube with six identical pressfit sides. I included indentations at all the inner corners so that the tabs would all fit together flush. I also included tabs to hold the cut out pieces in their places temporarily. This necessitated some postprocessing with a blade. I also used shallow cuts to mark places to secure the stock with screws. On the first attempt, the endmill did not cut all the way through the 1/2" plywood board, even though it had been zeroed and set properly.

The second time around, the machine did a much better job, especially because we used a down-spiral end mill (send chips down into the cut, making nice clean corners at the top) instead of an up-spiral.

The cube fit together nicely, but not as snugly as I should have liked. I did not use any interference in the pressfit dimensions and I may use 1 or 2 thousandths next time. The resulting 4" by 4" cube was not perfect (1/2" by 1/2" volumes were missing from two vertices) and I do not think that I could have made it so with identical sides.

Cup 'n Cake Mockup:

For my 2.009 project I am making a CNC baked goods decorator (in essence, a fancy icing machine). It is based of a design by Ilan Moyer. I am using ShopBot-cut parts to make the frame, mounts, and head.